1. Field
The following description relates to an apparatus and a method for estimating a state of charge (SoC) of a metal-air battery.
2. Description of Related Art
With an increase in emission of carbon dioxide due to consumption of fossil fuels and a dramatic change in crude oil prices, efforts to change an energy source for a vehicle from gasoline or diesel to electrical energy have been receiving attention.
Some electric vehicles have been commercialized, and lithium-ion batteries are expected to have a higher performance and be manufactured at a lower cost as a rechargeable battery for long-distance travel. However, currently used lithium-ion batteries have a restricted capacity and are unsuitable for long-distance travel. Thus, mounting a large quantity of the lithium-ion batteries on an electric vehicle may be necessary, and causing a price of the electric vehicle to increase considerably.
An energy density approximately six or seven times higher than a current energy density level is necessary to popularize electric vehicles. Thus, metal-air batteries, which, in theory, have a much higher energy density than lithium-ion batteries, are attracting interest.
A metal-air battery includes an anode, a cathode, an electrolyte, and a separation membrane. In the anode of the metal-air battery, an oxidation-reduction reaction of metal occurs. In the cathode of the metal-air battery, an oxidation-reduction reaction of oxygen flowing into the cathode from an outside source occurs. A theoretical energy density of the metal-air battery is significantly higher than other secondary batteries.
A conventional method of estimating a state of charge (SoC) of a battery in a conventional battery management system (BMS) includes integrating a current flowing in the battery and estimating the SoC of the battery based on the integrated current. However, such a method has an issue in that an accuracy of the estimating of the SoC decreases over time because errors that occur in a process of measuring a current are continuously accumulated.
Another conventional method of estimating an SoC of a battery includes measuring a voltage of a secondary battery, estimating an open circuit voltage (OCV) of the secondary battery in a no-load state based on the measured voltage, and estimating the SoC by referring to an SoC table for each OCV. However, such a method has an issue in that an accuracy in the estimating of the SoC decreases because increasing accuracy in the estimating of the OCV may not be easy during a charging and discharging state of the secondary battery.